Blind landing system



Sept. 16, 1952 G E, HART 2,611,124

BLIND LANDING SYSTEM Filed July 1, 1946 2 SHEETS-SHEET i TEE-i=1.

II I2 c I :5 24 25 AMPLIFIER ANTENNA I FILTER -28 RECEIVING ll MODULATORANTENNA PO ER T OSCILLATOR W ANTENNA AMPLIFIER RECEIVING lo MODULATORANTENNA FILTER 29 AMPLIFIER V ANTENNA INSTALLATION AT LANDING AREAINVENTOR.

GERALD E. HART ATTORNEY Sept. 16, 1952 HART 2,611,124

BLIND LANDING SYSTEM Filed July 1, 1946 2 SHEETS-SHEET 2 H :ElEI; 3RECEIVING IG ANTENNA FREQUENCY FILTER INSTALLATION 0N MIXER LANDINGCRAFT FREIEQREIN CY MIXER AMPLIFIER INTEGRAToR RANGE AMPL'F'ER DEvICEINDICATOR fi fi n LATERA MOD L L OSCILLATOR AMPLIFIER GUIDANCE ANTENNAINDICATOR INTEGRATCR ANTENNA AMPLIFIER DEVICE Low 7 FREQUENCY MIXER HIGHRECEIVING E MIXER I B 5 1,1524 I) C! LLI P LL yi//\/\ INVENTOR.

TIME GERALD E, HART TYPICAL FREQUENCY vARIATIoN wfi /x4 OF OSCILLATOR 3BY ATTORNEY Patented Sept. 16, 1952 UNITED STATES PATENT OFFICE BLINDLANDING SYSTEM Gerald E. Hart, United States Navy Application July 1,1946, Serial No. 680,787

' 4 Claims. (01. 343-6) (Granted under the act of March 3, 1883, as

This invention relates to blind landing approach systems, and inparticular to systems for determining the azimuthal position of anaircraft relative to a landing strip while the aircraft islanding. V

Variousblind landing systems have been proposed and utilized in thepast, however, these systems suffer from numerous disadvantages. In thesystems employing continual emission of elect-rical energy in two beamsfor determination of the azimuthal position of an incomin aircraft thedisadvantages are particularly objectionable. For such a system ofcontinual emission the average power requirements are considerable.

information. aboard an aircraft carrier or other platform subject tomotion, the dlfiiculty of maintaining the beams constant in thehorizontal plane is further aggravated by the motion of the platformwhich may cause rapid changes in the intensity of the signal received'atthe aircraft. 7

Accordingly it is an object of this invention to provide in a blindlanding apparatus an azimuthal-determination system havin minimum powerrequirements, to indicate to the pilot of an approaching aircraft theazimuthal position of his craft with respect to the landing platformduring a blind'landing approach.

Another object of this invention is to provide a method for supplyinglateral guidance during the flight of an aircraft,

A further object is to provide a system for accurately indicating thelateral position of an approaching aircraft relative to the landingplatform. f

A further object is to provide in a blind approach system an azimuthaldetermination system which can be employed to facilitate, the landin ofaircraft on a platform subject to motion.

Other and further objects present invention will become apparentupon acareful consideration of the following detailed description when takentogether with the acand features of the I amended April 30, 1928; 370 O.G. 757) companying drawings which illustrate a typical landing systemconstructed according tothe pr ne' ciples of the present invention,shown also is a flight path followed by an aircraft in seeking a landingline midway between the side boundaries of the landing platform.

Figure 2 shows, in part features of one embodiment of the invention,components shown therein preferably comprising the' installationinproximity to the landingplatform:

Figure 3 shows, in part, additional features of the one embodiment ofthe invention, components shown therein preferably comprising theinstallation aboard the landing craft.

Figure l shows a typical chart showing how. the frequency engendered byan oscillator used with this invention varies with time.

In accordance with the general concepts of the present invention a blindlanding approach sys-' tem is provided which will indicate to the pilotof an incoming plane the relative position of his aircraft with respectto a chosen dimension of the"landin'g-platform. Referring to Figure 1;

Ill.

devices as received in the 'aircraftlfl-are com"- bined in such a way asto produce a control signal dependent on the location of the aircraftwith respect to a line perpendicular to the line drawn through thelocations-of the responder devices I I and I2. An indicator operablefrom the control signals may be employed to provide the pilot withconvenient and accurate lateral guidance.

Referring now to Figure 2, a particular em bodiment of the features ofthe invention is shown comprising components located in proximity to thelanding platform l4 intended for the.

emission of signals in response to selected radiofrequency signals fromthe aircraft I0. Frequency modulated energy having typically thevariation characteristics as shown in Figure 4 is radiated from theaircraft II] for interception by the receiving antennas l5, I6 of theresponder devices II and I2. By way of example one of thebeaconstypified by H comprises a receiving antenna [5, modulator l1,filtering network [8,

amplifier l9, and an antenna, 20. Energyofthe selected frequency emittedfrom the aircraft I9 is intercepted by the: receiving antenna l5 and isapplied we balancedmodulator H. A lower frequency modulating signal of areference frequency, derived from an oscillation generator 2| is alsoapplied to the modulator H. The balanced modulator produces an outputsignal in which the carrier and modulating frequencies are suppressedbut in which the upper and lower side :band fre quency componentsarepresent. The voutput of the modulator I1 is applied to a frequencyselective network or filter I8 adapted to pass only 3,;-

selected band of frequencies, namely the sum frequency sideband, andreject the difference frequency sideband. The"sum frequency sig nals areamplified by a suitable power amplifier l9 and then applied to anantenna or radiating,- f

device20 having omnidirectional characteristicsv for radiation to theincoming aircraft.

Similarly, energy emitted from the aircraft: I9 is also received byantenna l6'and applied to a balanced modulator 22 where sum anddiference" e uenc v m ne s f .e;; c mi 1e;- ignal and .l-a signalromoscil ator 2 I 1 e pro:

uce A fi ter i s s ed-t r mit h p ssa e of the difference? frequencysideband-and rei t t e 1 m, f eque ,s b nd em oyed q-su p -the f iff r ne? fre u ncrsi nalt m,-

duces radio frequency; signals of su-flicientpowerr omn dir ct onal ration-bythe-an e na? 5. A par ith ref rence ie uencyener y en:

erated by oscillator ,2 is applied to a third power amplifier 26 toproduce energy; for radiation; by-

a third omnidirectional radiating antenna;v 22.

This reference frequency; energy is required in;

the aircraft receivin installation-J01;proper v l at o -p im nlsiemitted rom esp de devices l l, I2 as -.-Will be, explained later;The xact o tiqnof. th .radia te a: 21 is not.-

of extreme-importance;

I quency signal is produced is quite'complex, the; 25.

To reduce-the standby power-consumptionnof-.

the .unitn-to a minimum it is -desirable that the amplifiers and .24produce putput signals only. upon passage of the selected radiofrequency energy through-the filters J 8 and (i l-respectively. This is;normally .easy torealize with fixed-bias class B or C amplifi ers Stillrfurther;reduction in ;the standby power, consumption may be o.b,1-

amed-t y means-mic s n le: ne-pr.- a. ir 1 ines: nd nt rco nect n theower a the periods. of operation- 0f the amplifier- I9;- 24. Withreference to- FigurQN-B a typical arrangex. ment of componentseof theinvention installed in anaircraft isshown; Whenitis desired .to

obtain azimuthal information;- for landing; the normallyinoperativedevice of FigureB is turnedcn. ,,An. energy source 30 isthereby-set into, op.- v

rationr o p e Medicre uen y s a hearing selected modulation, typicallyof frequency, which is coupled to; an antenna-3] of anyticonventional.type having directive radiation char c e is cs ndso is qs d.on-t eaim at to-em 1. n r y nv a o wa r.e ion; elative' to he: flight of theaircraft. This interrogation signals emitted from ,antenna 3 I; actuatesthe landing.

la f rmis q pme t 2.- -3.-: re us1y; described,

f ergy a a 1 rheg po d n er s; L1 2 1 pm espons to e en r y; ec ive -zrom v source 30 is received at, {the aircraftinstallation:byamultiplejreceiving systemhavingthe input channels orreceivingantennas 32,33, 34. These.

three channels are preferably tuned,;respectively,='

to the, frequency ofq h gs gnal 'ie tted by each? of, the antennas20,131 21 and areidesignedto;

produc s g s, i d p n ency 1 .17 he-azimuthal:

4 position of the aircraft relative to the landing platform.

As typified by apparatus associated with the receiving antenna 32, whichis tuned to respond to energy of the sum frequency sideband emitted bytheantenna 20 received energy is; supplied a highn re ufin mixer. 3.5,,to e h r wi h energyfrom source 30. High frequency mixer 35; producessum and difference frequency '7 components of the signals from antenna32 and source 30. Following mixer 35 is a filtercircuit 36 which ispreferably tuned to respond to the difference frequency sideband in themixer output.;:- This difference frequency sideband is applied to anintermediate-frequency amplifier 31. Amplified signals from theamplifier 31, together with received; signals of reference frequencyfrom receivingantenna 33 are suppliedtoa low frequency mixer 38'resulting in the production of a aud o; req ency s gnal, the .-fr qu n yWhi his d pendent onithe: dista cenf-L-th air; craft ill from theradiatingantenna 2Q, r

The exact method 1 by t which this audio fregeneral method of,production is ;'alongl the following lines typical frequenciesbeinggiven. s

A typical operating carrier frequency produced; within the ;source 30 1would be 3000 megacycles p second. Thi I carrien-s snal q ency;-modulatedv over a;- typical bandwidth of 40--mc. The modulated energy isreceived by the receilv ing antennas 5; lfi-located near the landingplat form causing the emission of-energy byantennasi 0 1 5, 2 An e na.21, returnsnergy at" he: r quency he=.osci1 ator- 2 I wh h? ay be.-typically, 200 nc. "The ;energy returned by antenna 20 will-beatacarrier frequency-x3200:

me. and still frequency modulatedoveraeomc ing platform.

The 200 me. amplitude modulated carrier. signal is combineduin vthelowfrequencymixer 38 with the200 ,-mc., .signal from the oscillator; 2|.obtainedthrough the receiving channel 33 to; produce an audio frequencysignal, the actual I frequency of whichis variable in dependency on thedistance between theaircraft All] and the res sponder device I l.

The audio frequency Signal thus obtained .is: not used directly but isamplified in an audio,

frequency amplifier. .39 i tooperate. at suitable; in-

tegrating device 40 which produces a signal in, dependency on thefrequencythereof.. This in-" tegrated signal is compared with a similarsignal 1 obtained through apparatus associated with the input channel34, namely, high frequency mixer: 4 I, filter 42, intermediate frequencyamplifier low frequency mixer 44, amplifier 45 and'thein tegratingdevice 46. The combination of-these two integrated signals within anamplifier 41, which may "be of the -'D. C. type; produces an outputindication on the lateral: guidance vindicaw tor. 48:,toenablethe pilot=01 the approaching. rain:

craft H) to determine his azimuthal position relative to the selectedcenter line of the landing platform;

Thefrequencies involved in'the circuits associated with channel 34 aretreated in a manner similar to those in the circuits associated withchannel 32. One, important difference is present. The signalradiated byantenna in response to a signal from the antenna 3! is of a frequency of2800 me. This signal is similarly converted to a 200 me. withoutfrequency modulation but having low frequency amplitude modulation independency on the distance between platform l4 and craft Ifl.

An indication of (the distance between the landing platform I4 and theapproaching craft [0 is readily obtained by the addition of a rangeindicator 49 which may operate from the outputof either integratordevice. 40 or 46. Since the average frequency of the signals applied toamplifiers 39 and varies with the distance between platform 14 and"craft. III, the output signal from either integratordevice will vary indirect (dependency on this distance. The range indicatorf49, operativeto produce "a usable. signal i in accordance with the integrator outputsignal is a useful addition to the landing equipment.

From the foregoing discussion it is apparent that considerablemodification of the features of this invention is possible and while thedevice herein described and the form of apparatus for the operationthereof constitutes a preferred embodiment of the invention it is to beunderstood that the invention is not limited to this precise device andform of apparatus and that changes may be made therein without departingfrom the scope of the invention which is defined in the appended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. In a radiov directed approach system, azimuthal determinationapparatus for indicating the position of an approaching craft relativeto a selected line of approach to a particular locality, comprising;transmitting means aboard the craft for emitting a frequency varyingradio frequency signal bearing selected variation characteristics, afirst retransmitting means responsive to the radio frequency signal toemit a reference frequency signal, a second retransmitting meansresponsive to the radio frequency signal to produce a return signal offrequency equal to the sum of the radio frequency signal and thereference signal, a third retransmitting means physically removed fromthe second retransmitting means and responsive to the radio frequencysignal to produce a return signal of requency equal to the differencebetween the radio frequency and reference signals, receiver means aboardthe craft responsive to the energy from the retransmitting means, meansoperative from the output of the receiver means to produce first andsecond com parison signals in dependency on phase variation differencesbetween the radio frequency signal and the signals returned by thesecond and third retransmitting means produced by differences in lengthsof transmission paths, and means combining said comparison signals toproduce an indication in dependency on the azimuthal position of thecraft relative to the location of the second and third retransmittingmeans.

2. A radio directed approach system for accurately indicating theposition of an approaching craftrelative to a landing platform,comprising; energytransmitting means on the approach ing craft foremitting energy having selected modulation characteristics, a firstsignal generator located-in proximity to the landingplatform producing areference frequency signal, receiving means in proximity to the landingplatform for intercepting and amplifying energy emitted by thetransmitting means on the approaching craft, mixing means combining thesignal from said last named means and the reference frequency signal,first and second return transmitter means radiating, respectively, andfrom first and second different localities of the landing platform, thesum and difference fre-' quency components in the output from the mixingmeans, third return transmitter means for radiating the referencefrequency signal, receiver means intercepting and amplifying the returnsignals, combining means responsive to the return signals deriving afirst output signal in dependency on the distance of signal travelbetween the craft and of the radiation locality of the landing platformand a second output signal in dependency on the difference in the lengthof signal path between the craft and each of the first and secondlanding platform localities.

3. A radio directed approach system for accurately indicating theposition of an approaching craft relative to a landing platform,comprising; energy transmitting means on the approaching craft foremitting energy having selected modulation characteristics, a firstsignal generator located in proximity to the landing platform producinga reference frequency signal, receiving means in proximity to thelanding platform for intercepting and amplifying energy emitted by thetransmitting means on the approaching craft, first mixing meanscombining the signal from said last named means and the referencefrequency signal, first and second return transmitter means radiating,respectively, and from first and second different localities of thelanding platform, the sum and difference frequency components in theoutput from the first mixing means, third return transmitter means forradiating the reference frequency signal, receiver means interceptingand amplifying the return signals, first high frequency mixing meanscombining the received signal from the first return transmitter meanswith the signal generated by the energy transmission means to produce afirst beat signal of substantially the same frequency as the referencefrequency signal but bearing modulation in dependency on the time delayof transmission between the craft and the first return transmittermeans, first low frequency mixing means combining the received referencefrequency signal with the first beat signal to produce a firstintermediate output signal in dependency on the modulation of the firstbeat signal, second high frequency mixing means combining the receivedsignal from the second return transmitter means with the signalgenerated by the energy transmission means to produce a second beatsignal of substantially the same frequency as the reference frequencysignal but bearing modulation in dependency on the time delay oftransmission between the craft and the second return transmitter means,second low frequency mixer means combining the received referencefrequency signal with the first beat signal to reproduce a secondintermediate output signal in dependency on the modulation of the secondbeat signal, and integrator means combining the first and secondintermediate output signals to produce a distance indication inproportion to the distance between the craft and the'return transmittermeans and an azimuth indication in dependency on the difference in-thedistances between the craft and each of the first and second returntransmitter means.

4. In a radio directed approach system, azimuthal determinationapparatus for indicating the position of an approaching craft relativeto aselected line of approach to a landing area comprising; transmittingmeans aboard the craft 7 Number of the receiver means-to producefirstand second comparison signals in dependency on phaseyariaq tiondifferences between the radio frequency signal andthe second and thirdsignals produced by differences in' lengths of transmission paths, andmeans combining said comparison signals, to produce 'an indication'independency on the azimuthal position of the craft relative to the location 'of the retransmitting means.

i GERALDEHAR'IK' REFERENCES CIT D The following references'are of recordthe file of this patent: V

'UNITED'STATES r'A 'rmr'rs Name Q I v Date? 2,231,698 Nolde June 15';1943 2,405,238 Seeley Aug: 6,11946 2,405,239 See1ey' l Au .'6,1 19462,413,694 Dingley Jan.17 ,.;1947 2,427,219 Luck Sept; '9,"j1{9472,436,846 Williams Mar."2,' i 1948 2,524,050 Ginzton Oct.,3; 19502,528,119 Crosby 1 f Oct: 3 1," 1950

